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Gh. MS, Wilhelm MJ, Dai HL. Observing mechanosensitive channels in action in living bacteria. BIOPHYSICAL REPORTS 2024; 4:100141. [PMID: 38189030 PMCID: PMC10765490 DOI: 10.1016/j.bpr.2023.100141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 12/07/2023] [Indexed: 01/09/2024]
Abstract
Mechanosensitive (MS) channels act to protect the cytoplasmic membrane (CM) of living cells from environmental changes in osmolarity. In this report, we demonstrate the use of time-resolved second-harmonic light scattering (SHS) as a means of experimentally observing the relative state (open versus closed) of MS channels in living bacteria suspended in different buffer solutions. Specifically, the state of the MS channels was selectively controlled by changing the composition of the suspension medium, inducing either a transient or persistent osmotic shock. SHS was then used to monitor transport of the SHG-active cation, malachite green, across the bacterial CM. When MS channels were forced open, malachite green cations were able to cross the CM at a rate at least two orders of magnitude faster compared with when the MS channels were closed. These observations were corroborated using both numerical model simulations and complementary fluorescence experiments, in which the propensity for the CM impermeant cation, propidium, to stain cells was shown to be contingent upon the relative state of the MS channels (i.e., cells with open MS channels fluoresced red, cells with closed MS channels did not). Application of time-resolved SHS to experimentally distinguish MS channels opened via osmotic shock versus chemical activation, as well as a general comparison with the patch-clamp method is discussed.
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Affiliation(s)
| | | | - Hai-Lung Dai
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania
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2
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Beckham JL, Bradford TS, Ayala-Orozco C, Santos AL, Arnold D, van Venrooy AR, García-López V, Pal R, Tour JM. Distinguishing Molecular Mechanical Action from Photothermal and Photodynamic Behavior. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2306669. [PMID: 38062893 DOI: 10.1002/adma.202306669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Revised: 09/11/2023] [Indexed: 02/16/2024]
Abstract
Molecular motors (MM) are molecular machines, or nanomachines, that rotate unidirectionally upon photostimulation and perform mechanical work on their environment. In the last several years, it has been shown that the photomechanical action of MM can be used to permeabilize lipid bilayers, thereby killing cancer cells and pathogenic microorganisms and controlling cell signaling. The work contributes to a growing acknowledgement that the molecular actuation characteristic of these systems is useful for various applications in biology. However, the mechanical effects of molecular motion on biological materials are difficult to disentangle from photodynamic and photothermal action, which are also present when a light-absorbing fluorophore is irradiated with light. Here, an overview of the key methods used by various research groups to distinguish the effects of photomechanical, photodynamic, and photothermal action is provided. It is anticipated that this discussion will be helpful to the community seeking to use MM to develop new and distinctive medical technologies that result from mechanical disruption of biological materials.
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Affiliation(s)
- Jacob L Beckham
- Department of Chemistry, Rice University, 6100 Main Street MS 222, Houston, TX, 77005, USA
| | - Thomas S Bradford
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK
| | - Ciceron Ayala-Orozco
- Department of Chemistry, Rice University, 6100 Main Street MS 222, Houston, TX, 77005, USA
| | - Ana L Santos
- Department of Chemistry, Rice University, 6100 Main Street MS 222, Houston, TX, 77005, USA
- IdISBA-Fundación de Investigación Sanitaria de las Islas Baleares, Palma, 07120, Spain
| | - Dallin Arnold
- Department of Chemistry, Rice University, 6100 Main Street MS 222, Houston, TX, 77005, USA
| | - Alexis R van Venrooy
- Department of Chemistry, Rice University, 6100 Main Street MS 222, Houston, TX, 77005, USA
| | - Víctor García-López
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Robert Pal
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK
| | - James M Tour
- Department of Chemistry, Smalley-Curl Institute, NanoCarbon Center, Rice Advanced Materials Institute, Department of Materials Science and Nanoengineering, Department of Computer Science, Rice University, 6100 Main Street MS 222, Houston, TX, 77005, USA
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3
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Farzi K, Issler T, Unruh C, Prenner EJ. Gadolinium Effects on Liposome Fluidity and Size Depend on the Headgroup and Side Chain Structure of Key Mammalian Brain Lipids. Molecules 2023; 29:135. [PMID: 38202718 PMCID: PMC10780055 DOI: 10.3390/molecules29010135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Revised: 12/21/2023] [Accepted: 12/21/2023] [Indexed: 01/12/2024] Open
Abstract
The lanthanide metal gadolinium has been used in the healthcare industry as a paramagnetic contrast agent for years. Gadolinium deposition in brain tissue and kidneys has been reported following gadolinium-based contrast agent administration to patients undergoing MRI. This study demonstrates the detrimental effects of gadolinium exposure at the level of the cell membrane. Biophysical analysis using fluorescence spectroscopy and dynamic light scattering illustrates differential interactions of gadolinium ions with key classes of brain membrane lipids, including phosphatidylcholines and sphingomyelins, as well as brain polar extracts and biomimetic brain model membranes. Electrostatic attraction to negatively charged lipids like phosphatidylserine facilitates metal complexation but zwitterionic phosphatidylcholine and sphingomyelin interaction was also significant, leading to membrane rigidification and increases in liposome size. Effects were stronger for fully saturated over monounsaturated acyl chains. The metal targets key lipid classes of brain membranes and these biophysical changes could be very detrimental in biological membranes, suggesting that the potential negative impact of gadolinium contrast agents will require more scientific attention.
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Affiliation(s)
- Kianmehr Farzi
- Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada; (K.F.)
| | - Travis Issler
- Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada; (K.F.)
| | - Colin Unruh
- Fuel Innovation, Calgary, AB T2G 3K6, Canada;
| | - Elmar J. Prenner
- Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada; (K.F.)
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Ermakov YA. Electric Fields at the Lipid Membrane Interface. MEMBRANES 2023; 13:883. [PMID: 37999369 PMCID: PMC10673053 DOI: 10.3390/membranes13110883] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Revised: 11/13/2023] [Accepted: 11/14/2023] [Indexed: 11/25/2023]
Abstract
This review presents a comprehensive analysis of electric field distribution at the water-lipid membrane interface in the context of its relationship to various biochemical problems. The main attention is paid to the methodological aspects of bioelectrochemical techniques and quantitative analysis of electrical phenomena caused by the ionization and hydration of the membrane-water interface associated with the phase state of lipids. One of the objectives is to show the unique possibility of controlling changes in the structure of the lipid bilayer initiated by various membrane-active agents that results in electrostatic phenomena at the surface of lipid models of biomembranes-liposomes, planar lipid bilayer membranes (BLMs) and monolayers. A set of complicated experimental facts revealed in different years is analyzed here in order of increasing complexity: from the adsorption of biologically significant inorganic ions and phase rearrangements in the presence of multivalent cations to the adsorption and incorporation of pharmacologically significant compounds into the lipid bilayer, and formation of the layers of macromolecules of different types.
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Affiliation(s)
- Yury A Ermakov
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow 119071, Russia
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5
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Molotkovsky RJ, Galimzyanov TR, Ermakov YA. Heterogeneity in Lateral Distribution of Polycations at the Surface of Lipid Membrane: From the Experimental Data to the Theoretical Model. MATERIALS (BASEL, SWITZERLAND) 2021; 14:6623. [PMID: 34772149 PMCID: PMC8585412 DOI: 10.3390/ma14216623] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 10/26/2021] [Accepted: 10/29/2021] [Indexed: 11/16/2022]
Abstract
Natural and synthetic polycations of different kinds attract substantial attention due to an increasing number of their applications in the biomedical industry and in pharmacology. The key characteristic determining the effectiveness of the majority of these applications is the number of macromolecules adsorbed on the surface of biological cells or their lipid models. Their study is complicated by a possible heterogeneity of polymer layer adsorbed on the membrane. Experimental methods reflecting the structure of the layer include the electrokinetic measurements in liposome suspension and the boundary potential of planar bilayer lipid membranes (BLM) and lipid monolayers with a mixed composition of lipids and the ionic media. In the review, we systematically analyze the methods of experimental registration and theoretical description of the laterally heterogeneous structures in the polymer layer published in the literature and in our previous studies. In particular, we consider a model based on classical theory of the electrical double layer, used to analyze the available data of the electrokinetic measurements in liposome suspension with polylysines of varying molecular mass. This model suggests a few parameters related to the heterogeneity of the polymer layer and allows determining the conditions for its appearance at the membrane surface. A further development of this theoretical approach is discussed.
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Affiliation(s)
- Rodion J. Molotkovsky
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia;
| | | | - Yury A. Ermakov
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia;
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6
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MCAs in Arabidopsis are Ca 2+-permeable mechanosensitive channels inherently sensitive to membrane tension. Nat Commun 2021; 12:6074. [PMID: 34667173 PMCID: PMC8526687 DOI: 10.1038/s41467-021-26363-z] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 10/02/2021] [Indexed: 02/05/2023] Open
Abstract
Mechanosensitive (MS) ion channels respond to mechanical stress and convert it into intracellular electric and ionic signals. Five MS channel families have been identified in plants, including the Mid1-Complementing Activity (MCA) channel; however, its activation mechanisms have not been elucidated in detail. We herein demonstrate that the MCA2 channel is a Ca2+-permeable MS channel that is directly activated by membrane tension. The N-terminal 173 residues of MCA1 and MCA2 were synthesized in vitro, purified, and reconstituted into artificial liposomal membranes. Liposomes reconstituted with MCA1(1-173) or MCA2(1-173) mediate Ca2+ influx and the application of pressure to the membrane reconstituted with MCA2(1-173) elicits channel currents. This channel is also activated by voltage. Blockers for MS channels inhibit activation by stretch, but not by voltage. Since MCA proteins are found exclusively in plants, these results suggest that MCA represent plant-specific MS channels that open directly with membrane tension. Mechanosensitive ion channels convert mechanical stimuli into intracellular electric and ionic signals. Here the authors show that Arabidopsis MCA2 is a Ca2+-permeable mechanosensitive channel that is directly activated by membrane tension.
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Tunsirikongkon A, Pyo YC, Kim DH, Tran P, Park JS. Effect of calcium chloride on the protein encapsulation and stability of proliposomal granules. J Drug Deliv Sci Technol 2020. [DOI: 10.1016/j.jddst.2020.101672] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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8
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Ermakov YA, Sokolov VS, Akimov SA, Batishchev OV. Physicochemical and Electrochemical Aspects of the Functioning of Biological Membranes. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2020. [DOI: 10.1134/s0036024420030085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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9
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Galimzyanov TR, Bashkirov PV, Blank PS, Zimmerberg J, Batishchev OV, Akimov SA. Monolayerwise application of linear elasticity theory well describes strongly deformed lipid membranes and the effect of solvent. SOFT MATTER 2020; 16:1179-1189. [PMID: 31934707 DOI: 10.1039/c9sm02079a] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The theory of elasticity of lipid membranes is used widely to describe processes of cell membrane remodeling. Classically, the functional of a membrane's elastic energy is derived under assumption of small deformations; the membrane is considered as an infinitely thin film. This functional is quadratic on membrane surface curvature, with half of the splay modulus as its proportionality coefficient; it is generally applicable for small deformations only. Any validity of this functional for the regime of strong deformations should be verified experimentally. Recently, research using molecular dynamics simulations challenged the validity of this classic, linear model, i.e. the constancy of the splay modulus for strongly bent membranes. Here we demonstrate that the quadratic energy functional still can be applied for calculation of the elastic energy of strongly deformed membranes without introducing higher order terms with additional elastic moduli, but only if applied separately for each lipid monolayer. For cylindrical membranes, both classic and monolayerwise models yield equally accurate results. For cylindrical deformations we experimentally show that the elastic energy of lipid monolayers is additive: a low molecular weight solvent leads to an approximately twofold decrease in the membrane bending stiffness. Accumulation of solvent molecules in the inner monolayer of a membrane cylinder can explain these results, as the solvent partially prevents lipid molecules from splaying there. Thus, the linear theory of elasticity can be expanded through the range from weak to strong deformations-its simplicity and physical transparency describe various membrane phenomena.
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Affiliation(s)
- Timur R Galimzyanov
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, Moscow 119071, Russia
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10
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Reyes-Pardo H, Sánchez-Herrera DP. Mechanosensitive ion channel inhibitors promote the stiffening of the plasma membrane of mouse sensory neurons. SOFT MATTER 2019; 15:8320-8328. [PMID: 31565715 DOI: 10.1039/c9sm01230c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The mechanosensitivity of cells depends on the lipid-protein interactions of the plasma membrane. Affectations in the lipid region of the plasma membrane affect the transduction of mechanical forces, and any molecule that modifies the biophysical integrity of the lipid bilayer can alter the mechanical activity of the proteins inside the membrane. To understand whether inhibitors of mechanically activated ion channels affect the mechanical properties of the plasma membrane, we evaluated the rigidity of the membrane of sensory neurons of the DRG of mice using a variant of the scanning ion conductance microscopy method, which allows us to calculate the Young's modulus of individual cells before and after the perfusion of different doses of Gd3+, ruthenium red and GsMTx-4. Our results suggest that these molecules compromise the membrane by increasing the Young's modulus value, which indicates that the membrane becomes more rigid; these compounds act through different mechanisms and by a non-specific manner, each one shows a certain preference for specific cell subpopulations, depending on their cell size and their reactivity to isolectin B4. Our results support the idea that the biophysical properties that result from the interactions that arise in the membranes are part of the mechanotransduction process.
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Affiliation(s)
- Humberto Reyes-Pardo
- Unidad Monterrey, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apodaca, Nuevo León, Mexico.
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11
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Ermakov YA, Asadchikov VE, Roschin BS, Volkov YO, Khomich DA, Nesterenko AM, Tikhonov AM. Comprehensive Study of the Liquid Expanded-Liquid Condensed Phase Transition in 1,2-Dimyristoyl- sn-glycero-3-phospho-l-serine Monolayers: Surface Pressure, Volta Potential, X-ray Reflectivity, and Molecular Dynamics Modeling. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:12326-12338. [PMID: 31480848 DOI: 10.1021/acs.langmuir.9b01450] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
An integrated approach is applied to reveal fine changes in the surface-normal structure of 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS) monolayers at the air-lipid-water interface occurring in a liquid expanded (LE)-liquid condensed (LC) transition. The combination of the Langmuir monolayer technique, X-ray reflectometry, and molecular dynamics (MD) modeling provides new insight into the molecular nature of electrostatic phenomena in different stages of lipid compression. A homemade setup with a laboratory X-ray source (λ = 1.54 Å) offers a nondestructive way to reveal the structural difference between the LE and LC phases of the lipid. The electron density profile in the direction normal to the interface is recovered from the X-ray reflectivity data with the use of both model-independent and model-based approaches. MD simulations of the DMPS monolayer are performed for several areas per lipid using the all-atom force field. Using the conventional theory of capillary waves, a comparison is made between the electron density profiles reconstructed from the X-ray data and those calculated directly from MD modeling, which demonstrates remarkable agreement between the experiment and simulations for all selected lipid densities. This confirms the validity of the simulations and allows an analysis of the contributions of the hydrophobic tails and hydrated polar groups to the electron density profile and to the dipole component of the electric field at the interface. According to the MD data, the dependence of the Volta potential on the area per lipid in the monolayer has a different molecular nature below and above the phase transition. In the LE state of the monolayer, the potential is determined mostly by the oriented water molecules in the polar region of the lipid. In the LE-LC transition, these molecules are displaced to the bulk, and their effect on the Volta potential becomes insignificant compared with the contribution of the hydrophobic tails. The hydrophobic tails are highly ordered in the state of the liquid crystal so that their dipole moments entirely determine the growth of the potential upon compression up to the monolayer collapse.
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Affiliation(s)
- Yu A Ermakov
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences , Leninsky pr., 31/4 , Moscow 119071 , Russia
| | - V E Asadchikov
- Shubnikov Institute of Crystallography , Federal Research Center Crystallography and Photonics, Russian Academy of Sciences , Leninsky pr., 59 , Moscow 119333 , Russia
| | - B S Roschin
- Shubnikov Institute of Crystallography , Federal Research Center Crystallography and Photonics, Russian Academy of Sciences , Leninsky pr., 59 , Moscow 119333 , Russia
| | - Yu O Volkov
- Shubnikov Institute of Crystallography , Federal Research Center Crystallography and Photonics, Russian Academy of Sciences , Leninsky pr., 59 , Moscow 119333 , Russia
- Institute of Solid State Physics, Russian Academy of Sciences , Academician Ossipyan str. 2 , Moscow District, Chernogolovka 142432 , Russia
| | - D A Khomich
- Lomonosov Moscow State University , Biology Faculty, Leninskie gory 1/12 , Moscow 119234 , Russia
- Engelhardt Institute of Molecular Biology , Russian Academy of Sciences , Vavilova, 32 , Moscow 119991 , Russia
| | - A M Nesterenko
- Belozersky Institute of Physico-Chemical Biology , Lomonosov Moscow State University ; Leninskie gory 1/40 , Moscow , 119991 , Russia
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences , Miklukho-Maklaya 16/10 , Moscow 117997 , Russia
| | - A M Tikhonov
- Institute of Solid State Physics, Russian Academy of Sciences , Academician Ossipyan str. 2 , Moscow District, Chernogolovka 142432 , Russia
- Kapitza Institute for Physical Problems, Russian Academy of Sciences , ul. Kosygina 2 , Moscow 119334 , Russia
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How Plants Handle Trivalent (+3) Elements. Int J Mol Sci 2019; 20:ijms20163984. [PMID: 31426275 PMCID: PMC6719099 DOI: 10.3390/ijms20163984] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Revised: 08/12/2019] [Accepted: 08/13/2019] [Indexed: 12/31/2022] Open
Abstract
Plant development and fitness largely depend on the adequate availability of mineral elements in the soil. Most essential nutrients are available and can be membrane transported either as mono or divalent cations or as mono- or divalent anions. Trivalent cations are highly toxic to membranes, and plants have evolved different mechanisms to handle +3 elements in a safe way. The essential functional role of a few metal ions, with the possibility to gain a trivalent state, mainly resides in the ion's redox activity; examples are iron (Fe) and manganese. Among the required nutrients, the only element with +3 as a unique oxidation state is the non-metal, boron. However, plants also can take up non-essential trivalent elements that occur in biologically relevant concentrations in soils. Examples are, among others, aluminum (Al), chromium (Cr), arsenic (As), and antimony (Sb). Plants have evolved different mechanisms to take up and tolerate these potentially toxic elements. This review considers recent studies describing the transporters, and specific and unspecific channels in different cell compartments and tissues, thereby providing a global vision of trivalent element homeostasis in plants.
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13
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Molotkovsky RJ, Galimzyanov TR, Ermakov YA. Polypeptides on the Surface of Lipid Membranes. Theoretical Analysis of Electrokinetic Data. COLLOID JOURNAL 2019. [DOI: 10.1134/s1061933x19020108] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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14
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Pethő Z, Najder K, Bulk E, Schwab A. Mechanosensitive ion channels push cancer progression. Cell Calcium 2019; 80:79-90. [PMID: 30991298 DOI: 10.1016/j.ceca.2019.03.007] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 03/26/2019] [Accepted: 03/26/2019] [Indexed: 02/07/2023]
Abstract
In many cases, the mechanical properties of a tumor are different from those of the host tissue. Mechanical cues regulate cancer development by affecting both tumor cells and their microenvironment, by altering cell migration, proliferation, extracellular matrix remodeling and metastatic spread. Cancer cells sense mechanical stimuli such as tissue stiffness, shear stress, tissue pressure of the extracellular space (outside-in mechanosensation). These mechanical cues are transduced into a cellular response (e. g. cell migration and proliferation; inside-in mechanotransduction) or to a response affecting the microenvironment (e. g. inducing a fibrosis or building up growth-induced pressure; inside-out mechanotransduction). These processes heavily rely on mechanosensitive membrane proteins, prominently ion channels. Mechanosensitive ion channels are involved in the Ca2+-signaling of the tumor and stroma cells, both directly, by mediating Ca2+ influx (e. g. Piezo and TRP channels), or indirectly, by maintaining the electrochemical gradient necessary for Ca2+ influx (e. g. K2P, KCa channels). This review aims to discuss the diverse roles of mechanosenstive ion channels in cancer progression, especially those involved in Ca2+-signaling, by pinpointing their functional relevance in tumor pathophysiology.
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Affiliation(s)
- Zoltán Pethő
- Institut für Physiologie II, Robert-Koch-Str. 27b, 48149 Münster, Germany.
| | - Karolina Najder
- Institut für Physiologie II, Robert-Koch-Str. 27b, 48149 Münster, Germany
| | - Etmar Bulk
- Institut für Physiologie II, Robert-Koch-Str. 27b, 48149 Münster, Germany
| | - Albrecht Schwab
- Institut für Physiologie II, Robert-Koch-Str. 27b, 48149 Münster, Germany
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15
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Ermakov YA, Kamaraju K, Dunina-Barkovskaya A, Vishnyakova KS, Yegorov YE, Anishkin A, Sukharev S. High-Affinity Interactions of Beryllium(2+) with Phosphatidylserine Result in a Cross-Linking Effect Reducing Surface Recognition of the Lipid. Biochemistry 2017; 56:5457-5470. [PMID: 28872302 DOI: 10.1021/acs.biochem.7b00644] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Beryllium has multiple industrial applications, but its manufacture is associated with a serious occupational risk of developing chronic inflammation in the lungs known as berylliosis, or chronic beryllium disease. Although the Be2+-induced abnormal immune responses have recently been linked to a specific MHC-II allele, the nature of long-lasting granulomas is not fully understood. Here we show that Be2+ binds with a micromolar affinity to phosphatidylserine (PS), the major surface marker of apoptotic cells. Isothermal titration calorimetry indicates that, like that of Ca2+, binding of Be2+ to PS liposomes is largely entropically driven, likely by massive desolvation. Be2+ exerts a compacting effect on PS monolayers, suggesting cross-linking through coordination by both phosphates and carboxyls in multiple configurations, which were visualized in molecular dynamics simulations. Electrostatic modification of PS membranes by Be2+ includes complete neutralization of surface charges at ∼30 μM, accompanied by an increase in the boundary dipole potential. The data suggest that Be2+ can displace Ca2+ from the surface of PS, and being coordinated in a tight shell of four oxygens, it can mask headgroups from Ca2+-mediated recognition by PS receptors. Indeed, 48 μM Be2+ added to IC-21 cultured macrophages specifically suppresses binding and engulfment of PS-coated silica beads or aged erythrocytes. We propose that Be2+ adsorption at the surface of apoptotic cells may potentially prevent normal phagocytosis, thus causing accumulation of secondary necrotic foci and the resulting chronic inflammation.
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Affiliation(s)
- Yuri A Ermakov
- Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences , Leninsky Prospect 31, Moscow 117071, Russia
| | - Kishore Kamaraju
- Department of Biology, University of Maryland , College Park, Maryland 20742, United States
| | | | - Khava S Vishnyakova
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences , Vavilov Street 32, Moscow 119991, Russia
| | - Yegor E Yegorov
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences , Vavilov Street 32, Moscow 119991, Russia
| | - Andriy Anishkin
- Department of Biology, University of Maryland , College Park, Maryland 20742, United States
| | - Sergei Sukharev
- Department of Biology, University of Maryland , College Park, Maryland 20742, United States
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Maneshi MM, Sachs F, Hua SZ. A Threshold Shear Force for Calcium Influx in an Astrocyte Model of Traumatic Brain Injury. J Neurotrauma 2015; 32:1020-9. [PMID: 25442327 DOI: 10.1089/neu.2014.3677] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Traumatic brain injury (TBI) refers to brain damage resulting from external mechanical force, such as a blast or crash. Our current understanding of TBI is derived mainly from in vivo studies that show measurable biological effects on neurons sampled after TBI. Little is known about the early responses of brain cells during stimuli and which features of the stimulus are most critical to cell injury. We generated defined shear stress in a microfluidic chamber using a fast pressure servo and examined the intracellular Ca(2+) levels in cultured adult astrocytes. Shear stress increased intracellular Ca(2+) depending on the magnitude, duration, and rise time of the stimulus. Square pulses with a fast rise time (∼2 ms) caused transient increases in intracellular Ca(2+), but when the rise time was extended to 20 ms, the response was much less. The threshold for a response is a matrix of multiple parameters. Cells can integrate the effect of shear force from repeated challenges: A pulse train of 10 narrow pulses (11.5 dyn/cm(2) and 10 ms wide) resulted in a 4-fold increase in Ca(2+) relative to a single pulse of the same amplitude 100 ms wide. The Ca(2+) increase was eliminated in Ca(2+)-free media, but was observed after depleting the intracellular Ca(2+) stores with thapsigargin suggesting the need for a Ca(2+) influx. The Ca(2+) influx was inhibited by extracellular Gd(3+), a nonspecific inhibitor of mechanosensitive ion channels, but it was not affected by the more specific inhibitor, GsMTx4. The voltage-gated channel blockers, nifedipine, diltiazem, and verapamil, were also ineffective. The data show that the mechanically induced Ca(2+) influx commonly associated with neuron models for TBI is also present in astrocytes, and there is a viscoelastic/plastic coupling of shear stress to the Ca(2+) influx. The site of Ca(2+) influx has yet to be determined.
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Affiliation(s)
| | - Frederick Sachs
- 2 Department of Physiology and Biophysics, SUNY-Buffalo , Buffalo, New York
| | - Susan Z Hua
- 1 Department of Mechanical and Aerospace Engineering, SUNY-Buffalo , Buffalo, New York.,2 Department of Physiology and Biophysics, SUNY-Buffalo , Buffalo, New York
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Zeng J, Eckenrode HM, Dai HL, Wilhelm MJ. Adsorption and transport of charged vs. neutral hydrophobic molecules at the membrane of murine erythroleukemia (MEL) cells. Colloids Surf B Biointerfaces 2015; 127:122-9. [DOI: 10.1016/j.colsurfb.2015.01.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 01/07/2015] [Accepted: 01/08/2015] [Indexed: 11/25/2022]
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18
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Gianulis EC, Pakhomov AG. Gadolinium modifies the cell membrane to inhibit permeabilization by nanosecond electric pulses. Arch Biochem Biophys 2015; 570:1-7. [PMID: 25707556 DOI: 10.1016/j.abb.2015.02.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 02/12/2015] [Accepted: 02/16/2015] [Indexed: 11/18/2022]
Abstract
Lanthanide ions are the only known blockers of permeabilization by electric pulses of nanosecond duration (nsEP), but the underlying mechanisms are unknown. We employed timed applications of Gd(3+) before or after nsEP (600-ns, 20 kV/cm) to investigate the mechanism of inhibition, and measured the uptake of the membrane-impermeable YO-PRO-1 (YP) and propidium (Pr) dyes. Gd(3+) inhibited dye uptake in a concentration-dependent manner. The inhibition of Pr uptake was always about 2-fold stronger. Gd(3+) was effective when added after nsEP, as well as when it was present during nsEP exposure and removed afterward. Pores formed by nsEP in the presence of Gd(3+) remained quiescent unless Gd(3+) was promptly washed away. Such pores resealed (or shrunk) shortly after the wash despite the absence of Gd(3+). Finally, a brief (3s) Gd(3+) perfusion was equally potent at inhibiting dye uptake when performed either immediately before or after nsEP, or early before nsEP. The persistent protective effect of Gd(3+) even in its absence proves that inhibition by Gd(3+) does not result from simple pore obstruction. Instead, Gd(3+) causes lasting modification of the membrane, occurring promptly and irrespective of pore presence; it makes the membrane less prone to permeabilization and/or reduces the stability of electropores.
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Affiliation(s)
- Elena C Gianulis
- Frank Reidy Research Center for Bioelectrics, Old Dominion University, Norfolk, VA, 23508, USA.
| | - Andrei G Pakhomov
- Frank Reidy Research Center for Bioelectrics, Old Dominion University, Norfolk, VA, 23508, USA
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19
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Marukovich NI, Nesterenko AM, Ermakov YA. Structural factors of lysine and polylysine interaction with lipid membranes. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2015. [DOI: 10.1134/s1990747814060038] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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20
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Awad D, Bartok M, Mostaghimi F, Schrader I, Sudumbrekar N, Schaffran T, Jenne C, Eriksson J, Winterhalter M, Fritz J, Edwards K, Gabel D. Halogenated Dodecaborate Clusters as Agents to Trigger Release of Liposomal Contents. Chempluschem 2015; 80:656-664. [DOI: 10.1002/cplu.201402286] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2014] [Revised: 12/07/2014] [Indexed: 11/12/2022]
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21
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Basson MD, Zeng B, Downey C, Sirivelu MP, Tepe JJ. Increased extracellular pressure stimulates tumor proliferation by a mechanosensitive calcium channel and PKC-β. Mol Oncol 2014; 9:513-26. [PMID: 25454347 DOI: 10.1016/j.molonc.2014.10.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Revised: 10/17/2014] [Accepted: 10/20/2014] [Indexed: 01/31/2023] Open
Abstract
Large tumors exhibit high interstitial pressure heightened by growth against the constraining stroma. Such pressures could stimulate tumor proliferation via a mechanosensitive ion channel. We studied the effects of 0-80 mmHg increased extracellular pressure for 24 h on proliferation of SW620, Caco-2, and CT-26 colon; MCF-7 breast; and MLL and PC3 prostate cancer cells, and delineated its mechanism in SW620 cells with specific inhibitors and siRNA. Finally, we compared NF-kB, phospho-IkB and cyclin D1 immunoreactivity in the high pressure centers and low pressure peripheries of human tumors. Pressure-stimulated proliferation in all cells. Pressure-driven SW620 proliferation required calcium influx via the T-type Ca(2+) channel Cav3.3, which stimulated PKC-β to invoke the IKK-IkB-NF-kB pathway to increase proliferation and S-phase fraction. The mitotic index and immunoreactivity of NF-kB, phospho-IkB, and cyclin D1 in the center of 28 large human colon, lung, and head and neck tumors exceeded that in tumor peripheries. Extracellular pressure increases [Ca(2+)]i via Cav3.3, driving a PKC-β- IKK- IkB-NF-kB pathway that stimulates cancer cell proliferation. Rapid proliferation in large stiff tumors may increase intratumoral pressure, activating this pathway to stimulate further proliferation in a feedback cycle that potentiates tumor growth. Targeting this pathway may inhibit proliferation in large unresectable tumors.
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Affiliation(s)
- Marc D Basson
- Department of Surgery, Michigan State University College of Human Medicine, 1200 E Michigan Ave, Lansing Charter Township, MI 48912, USA.
| | - Bixi Zeng
- Department of Surgery, Michigan State University College of Human Medicine, 1200 E Michigan Ave, Lansing Charter Township, MI 48912, USA
| | - Christina Downey
- Department of Surgery, Michigan State University College of Human Medicine, 1200 E Michigan Ave, Lansing Charter Township, MI 48912, USA
| | - Madhu P Sirivelu
- Department of Surgery, Michigan State University College of Human Medicine, 1200 E Michigan Ave, Lansing Charter Township, MI 48912, USA
| | - Jetze J Tepe
- Department of Pharmacology, Michigan State University, 1355 Bogue Street, B440 Life Sciences Building, East Lansing, MI 48824, USA
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22
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Bending rigidity of phosphatidylserine-containing lipid bilayers in acidic aqueous solutions. Colloids Surf A Physicochem Eng Asp 2014. [DOI: 10.1016/j.colsurfa.2013.12.059] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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23
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He Y, Prieto L, Lazaridis T. Modeling peptide binding to anionic membrane pores. J Comput Chem 2013; 34:1463-75. [PMID: 23580260 DOI: 10.1002/jcc.23282] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 02/14/2013] [Accepted: 03/04/2013] [Indexed: 02/04/2023]
Abstract
Peptide-induced pore formation in membranes can be dissected into two steps: pore formation and peptide binding to the pore. A computational method is proposed to study the second step in anionic membranes. The electrostatic potential is obtained from numerical solutions to the Poisson-Boltzmann equation and is then used in conjunction with IMM1 (implicit membrane model 1). A double charge layer model is used to incorporate the effects of the membrane dipole potential. Inhomogeneity of the charge density in the pore, characterized by explicit membrane simulations of toroidal pores, is included in the model. This approach was applied to two extensively studied peptides, magainin and melittin. In agreement with previous work, binding to toroidal pores is more favorable than binding to the flat membrane. The dependence of binding energy on anionic content exhibits different patterns for the two peptides, in correlation with the different lipid selectivity that has been observed experimentally.
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Affiliation(s)
- Yi He
- Department of Chemistry, City College of New York, New York, New York 10031, USA
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24
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Nesterenko AM, Ermakov YA. Molecular-dynamic simulation of phospholipid bilayers: Ion distribution at the surface of neutral and charged bilayer in the liquid crystalline state. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2013. [DOI: 10.1134/s1990747812050145] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Charged Lipid Bilayers in Aqueous Surroundings with Low pH. ACTA ACUST UNITED AC 2013. [DOI: 10.1016/b978-0-12-411515-6.00001-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Sukharev S, Sachs F. Molecular force transduction by ion channels: diversity and unifying principles. J Cell Sci 2012; 125:3075-83. [PMID: 22797911 DOI: 10.1242/jcs.092353] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cells perceive force through a variety of molecular sensors, of which the mechanosensitive ion channels are the most efficient and act the fastest. These channels apparently evolved to prevent osmotic lysis of the cell as a result of metabolite accumulation and/or external changes in osmolarity. From this simple beginning, nature developed specific mechanosensitive enzymes that allow us to hear, maintain balance, feel touch and regulate many systemic variables, such as blood pressure. For a channel to be mechanosensitive it needs to respond to mechanical stresses by changing its shape between the closed and open states. In that way, forces within the lipid bilayer or within a protein link can do work on the channel and stabilize its state. Ion channels have the highest turnover rates of all enzymes, and they can act as both sensors and effectors, providing the necessary fluxes to relieve osmotic pressure, shift the membrane potential or initiate chemical signaling. In this Commentary, we focus on the common mechanisms by which mechanical forces and the local environment can regulate membrane protein structure, and more specifically, mechanosensitive ion channels.
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Affiliation(s)
- Sergei Sukharev
- Department of Biology, University of Maryland, College Park, MD 20742, USA.
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Ermakov YA. Relationships between electrostatic and mechanical characteristics of dimyristoylphosphatidylserine monolayer. BIOCHEMISTRY (MOSCOW) SUPPLEMENT SERIES A: MEMBRANE AND CELL BIOLOGY 2011. [DOI: 10.1134/s1990747811050059] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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29
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Nesterenko AM, Krasilnikov PM, Ermakov YA. Molecular-dynamic simulation of DPPC bilayer in different phase state: Hydration and electric field distribution in the presence of Be2+ cations. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2011. [DOI: 10.1134/s1990747811050084] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Kitani R, Kakehata S, Kalinec F. Motile responses of cochlear outer hair cells stimulated with an alternating electrical field. Hear Res 2011; 280:209-18. [PMID: 21664265 DOI: 10.1016/j.heares.2011.05.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2011] [Revised: 05/19/2011] [Accepted: 05/20/2011] [Indexed: 10/18/2022]
Abstract
The goal of the present study was to evaluate and characterize the motile responses of guinea pig OHCs, stimulated at frequencies varying from 50 Hz to 4 kHz, using high-definition, high-speed video recording and fully automatic image analysis software. Cells stimulated in continuous, burst and sweeping modes with an external alternating electrical field showed robust fast and slow motility, which were dependent on frequency, mode and intensity of stimulation. In response to continuous stimulation, electromotile amplitude ranged from 0.3% to 3.2% of total cell length, whereas cell length usually decreased in amounts varying from 0.1% to 4.3%. Electromotile amplitude in OHCs stimulated with square wave's sweeps was near constant up to 200 Hz, progressively decreased between 200 Hz and 2 kHz, and then remained constant up to 4 kHz. In continuous and burst modes electromotility followed cycle-by-cycle the electrical stimulus, but it required 1-2 s to fully develop and reach maximal amplitude. Instead, slow cell length changes started about 0.6 s after the beginning and continuously developed up to 3 s after the end of electrical stimulation. Incubation of OHCs with 10 mM salicylate affected electromotility but not slow motility, whereas incubation with 3 mM gadolinium affected both. Thus, combination of external electrical stimulation, high-speed video recording and advanced image analysis software provides information about OHC motile responses at acoustic frequencies with an unprecedented detail, opening new areas of research in the field of OHC mechanics.
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Affiliation(s)
- Rei Kitani
- Division of Cell Biology and Genetics, House Ear Institute, 2100 West 3rd Street Los Angeles, CA 90057, USA
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31
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Ermakov YA, Kamaraju K, Sengupta K, Sukharev S. Gadolinium ions block mechanosensitive channels by altering the packing and lateral pressure of anionic lipids. Biophys J 2010; 98:1018-27. [PMID: 20303859 PMCID: PMC2849073 DOI: 10.1016/j.bpj.2009.11.044] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2009] [Revised: 11/20/2009] [Accepted: 11/25/2009] [Indexed: 11/28/2022] Open
Abstract
Effects of polyvalent ions on the lateral packing of phospholipids have been known for decades, but the physiological consequences have not been systematically studied. Gd(3+) is a relatively nonspecific agent that blocks mechano-gated channels with a variable affinity. In this study, we show that the large mechanosensitive channel MscL of Escherichia coli is effectively blocked by Gd(3+) only when reconstituted with negatively charged phospholipids (e.g., PS). Taking this lead, we studied effects of Gd(3+) on monolayers and unilamellar vesicles made of natural brain PS, DMPS, and its mixtures with DMPC. In monolayer experiments, we found that muM Gd(3+) present in the subphase leads to approximately 8% lateral compaction of brain PS (at 35 mN/m). Gd(3+) more strongly shrinks and rigidifies DMPS films causing a spontaneous liquid expanded-to-compact transition to the limiting 40 A(2)/mol. Pressure-area isotherms of uncharged DMPC were unaffected by Gd(3+), and neutralization of DMPS surface by low pH did not produce strong compaction. Upshifts of surface potential isotherms of DMPS monolayers reflected changes in the diffuse double layer due to neutralization of headgroup charges by Gd(3+), whereas the increased packing density produced up to a 200 mV change in the interfacial dipole potential. The slopes of surface potential versus reciprocal area predicted that Gd(3+) induced a modest ( approximately 18%) increase in the magnitude of the individual lipid dipoles in DMPS. Isothermal titration calorimetry indicated that binding of Gd(3+) to DMPS liposomes in the gel state is endothermic, whereas binding to liquid crystalline liposomes produces heat consistent with the isothermal liquid-to-gel phase transition induced by the ion. Both titration curves suggested a K(b) of approximately 10(6) M(-1). We conclude that anionic phospholipids serve as high-affinity receptors for Gd(3+) ions, and the ion-induced compaction generates a lateral pressure increase estimated as tens of mN/m. This pressure can "squeeze" the channel and shift the equilibrium toward the closed state.
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Key Words
- dmpc, dimirystoyl phosphatidylcholine
- dmps, dimirystoyl phosphatidylserine
- edl, electric double layer
- gcs, gouy-chapman-stern approximation
- gd3+, gadolinium
- itc, isothermal titration calorimetry
- le-lc transition, liquid expanded–liquid compact transition
- mscl, mechanosensitive channel of large conductance
- mscs, mechanosensitive channel of small conductance
- pc, phosphatidylcholine
- pe, phosphatidylethanolamine
- ps, phosphatidylserine
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Affiliation(s)
- Yury A. Ermakov
- The Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia
| | - Kishore Kamaraju
- Department of Biology, University of Maryland, College Park, Maryland
| | - Krishnendu Sengupta
- Indian Association for the Cultivation of Sciences, Kolkata, West Bengal, India
| | - Sergei Sukharev
- Department of Biology, University of Maryland, College Park, Maryland
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32
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Cloning and functional expression of an MscL ortholog from Rhizobium etli: characterization of a mechanosensitive channel. J Membr Biol 2010; 234:13-27. [PMID: 20177670 DOI: 10.1007/s00232-010-9235-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Accepted: 01/26/2010] [Indexed: 10/19/2022]
Abstract
Rhizobium etli is equipped with several systems to handle both hyper- and hypo-osmotic stress. For adaptation to hypo-osmotic stress, R. etli possesses a single gene with clear homology to MscS, four MscS-like channels and one ortholog of MscL (ReMscL, identity approximately 44% compared to Escherichia coli MscL). We subcloned and expressed the ReMscL channel ortholog from R. etli in E. coli to examine its activity by patch clamp in giant spheroplasts and characterized it at the single-channel level. We obtained evidence that ReMscL prevents the lysis of E. coli null mutant log-phase cells upon a rapid, osmotic downshock and identified a slight pH dependence for ReMscL activation. Here, we describe the facilitation of ReMscL activation by arachidonic acid (AA) and a reversible inhibitory effect of Gd(3+). The results obtained in these experiments suggest a stabilizing effect of micromolar AA and traces of Gd(3+) ions in the partially expanded conformation of the protein. Finally, we discuss a possible correlation between the number of gene paralogs for MS channels and the habitats of several microorganisms. Taken together, our data show that ReMscL may play an important role in free-living rhizobacteria during hypo-osmotic shock in the rhizosphere.
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Abstract
Mechanosensitive ion channels (MSCs) exist in all cells, but mechanosensitivity is a phenotype not a genotype. Specialized mechanoreceptors such as the hair cells of the cochlea require elaborate mechanical impedance matching to couple the channels to the external stress. In contrast, MSCs in nonspecialized cells appear activated by stress in the bilayer local to the channel--within about three lipids. Local mechanical stress can be produced by far-field tension, amphipaths, phase separations, the cytoskeleton, the extracellular matrix, and the adhesion energy between the membrane and a patch pipette. Understanding MSC function requires under standing the stimulus.
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34
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Bostick DL, Brooks CL. Statistical determinants of selective ionic complexation: ions in solvent, transport proteins, and other "hosts". Biophys J 2009; 96:4470-92. [PMID: 19486671 DOI: 10.1016/j.bpj.2009.03.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Revised: 03/09/2009] [Accepted: 03/11/2009] [Indexed: 10/20/2022] Open
Abstract
To provide utility in understanding the molecular evolution of ion-selective biomembrane channels/transporters, globular proteins, and ionophoric compounds, as well as in guiding their modification and design, we present a statistical mechanical basis for deconstructing the impact of the coordination structure and chemistry of selective multidentate ionic complexes. The deconstruction augments familiar ideas in liquid structure theory to realize the ionic complex as an open ion-ligated system acting under the influence of an "external field" provided by the host (or surrounding medium). Using considerations derived from this basis, we show that selective complexation arises from exploitation of a particular ion's coordination preferences. These preferences derive from a balance of interactions much like that which dictates the Hofmeister effect. By analyzing the coordination-state space of small family IA and VIIA ions in simulated fluid media, we derive domains of coordinated states that confer selectivity for a given ion upon isolating and constraining particular attributes (order parameters) of a complex comprised of a given type of ligand. We demonstrate that such domains may be used to rationalize the ion-coordinated environments provided by selective ionophores and biological ion channels/transporters of known structure, and that they can serve as a means toward deriving rational design principles for ion-selective hosts.
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Affiliation(s)
- David L Bostick
- Department of Chemistry and Program in Biophysics, The University of Michigan, Ann Arbor, Michigan, USA
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Hurst AC, Gottlieb PA, Martinac B. Concentration dependent effect of GsMTx4 on mechanosensitive channels of small conductance in E. coli spheroplasts. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 38:415-25. [PMID: 19132368 DOI: 10.1007/s00249-008-0386-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2008] [Revised: 11/19/2008] [Accepted: 11/25/2008] [Indexed: 10/21/2022]
Abstract
The spider peptide GsMTx4, at saturating concentration of 5 muM, is an effective and specific inhibitor for stretch-activated mechanosensitive (MS) channels found in a variety of eukaryotic cells. Although the structure of the peptide has been solved, the mode of action remains to be determined. Because of its amphipathic structure, the peptide is proposed to interact with lipids at the boundaries of the MS channel proteins. In addition, GsMTx4 has antimicrobial effects, inhibiting growth of several species of bacteria in the range of 5-64 microM. Previous studies on prokaryotic MS channels, which serve as model systems to explore the principle of MS channel gating, have shown that various amphipathic compounds acting at the protein-lipid interface affect MS channel gating. We have therefore analyzed the effect of different concentrations of extracellular GsMTx4 on MS channels of small conductance, MscS and MscK, in the cytoplasmic membrane of wild-type E. coli spheroplasts using the patch-clamp technique. Our study shows that the peptide GsMTx4 exhibits a biphasic response in which peptide concentration determines inhibition or potentiation of activity in prokaryotic MS channels. At low peptide concentrations of 2 and 4 microM the gating of the prokaryotic MS channels was hampered, manifested by a decrease in pressure sensitivity. In contrast, application of peptide at concentrations of 12 and 20 microM facilitated prokaryotic MS channel opening by increasing the pressure sensitivity.
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Affiliation(s)
- Annette C Hurst
- Molecular Biophysics Laboratory, School of Biomedical Sciences, University of Queensland, St Lucia, QLD, 4072, Australia
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36
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Single-molecule investigation of the influence played by lipid rafts on ion transport and dynamic features of the pore-forming alamethicin oligomer. J Membr Biol 2008; 224:45-54. [PMID: 18850058 DOI: 10.1007/s00232-008-9131-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Accepted: 09/18/2008] [Indexed: 12/29/2022]
Abstract
In this experimental work we employed single-molecule electrical recordings on alamethicin oligomers inserted in lipid bilayers made of brain sphingomyelin (bSM), palmitoyloleoylphosphatidylcholine (POPC) and cholesterol (chol) to unravel novel aspects regarding lipid raft interactions with pore-forming peptides. We probed the effect of lipid rafts on electrical properties of inserted alamethicin oligomers, and our data convincingly prove that the single-channel electrical conductance of various subconductance states of the alamethicin oligomer (1) increases in the presence of raft-containing ternary lipid mixtures (POPC-chol-bSM) compared to cases when bilayers were made of POPC-chol and POPC and (2) decreases in the presence of raft-containing ternary lipid mixtures compared to nonraft ternary mixtures which favor the fluid and liquid ordered phases alone. Our data demonstrate that the presence of lipid rafts leads to a slower association kinetics of alamethicin oligomers, seemingly reflecting a slower lateral diffusion process of such peptide aggregates compared to the case of nonraft, binary lipid mixtures. Furthermore, we show that the electrical capacitance of ternary lipid mixtures (POPC-chol-bSM) decreases in the presence of raft domains by comparison to nonraft binary phases (POPC-chol) or POPC alone, and this could constitute an additional mechanism via which macroscopic electrical manifestations of eukaryotic cells are modulated by the coexistence of gel and fluid domains of the plasma membrane.
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Finogenova OA, Filinsky DV, Ermakov YA. Electrostatic effects upon adsorption and desorption of polylysines on the surface of lipid membranes of different composition. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2008. [DOI: 10.1134/s1990747808020128] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Influence of Integrin-blocking Peptide on Gadolinium- and Hypertonic Shrinking-induced Neurotransmitter Release in Rat Brain Synaptosomes. Neurochem Res 2008; 33:1316-24. [DOI: 10.1007/s11064-007-9585-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Accepted: 12/27/2007] [Indexed: 11/26/2022]
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Gottlieb PA, Suchyna TM, Sachs F. Properties and Mechanism of the Mechanosensitive Ion Channel Inhibitor GsMTx4, a Therapeutic Peptide Derived from Tarantula Venom. CURRENT TOPICS IN MEMBRANES 2007; 59:81-109. [PMID: 25168134 DOI: 10.1016/s1063-5823(06)59004-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Mechanosensitive ion channels (MSCs) are found in all types of cells ranging from Escherichia coli to morning glories to humans. They seem to fall into two families: those in specialized receptors, such as the hair cells of the cochlea, and those in cells not clearly differentiated for sensory duty. The physiological function of the channels in nonspecialized cells has not been demonstrated, although their activity has been demonstrated innumerable times in vitro. The only specific reagent to block MSCs isGsMTx4, a 4-kDa peptide isolated from tarantula venom. Despite being isolated from venom, it is nontoxic to mice. GsMTx4 is specific for an MSC subtype, the nonselective cation channels that may be members of the transient receptor potential (TRP) family. GsMTx4 acts as a gating modifier, increasing the energy of the open state relative to the closed state. The mirror image D enantiomer of GsMTx4 is equally active, so mode of action is not via the traditional lock and key model. GsMTx4 probably acts in the boundary lipid of the channel by changing local curvature and mechanically stressing the channel toward the closed state. Despite the lack of definitive physiological data on the function of the cationic MSCs, GsMTx4 may prove useful as a drug or lead compound that can affect physiological processes. These processes would be those driven by mechanical stress, such as blood vessel autoregulation, stress-induced contraction of smooth muscle, and Ca(2+) loading in muscular dystrophy.
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Affiliation(s)
- Philip A Gottlieb
- The Department of Physiology and Biophysics, Center for Single Molecule Biophysics, SUNY at Buffalo, Buffalo, New York 14214
| | - Thomas M Suchyna
- The Department of Physiology and Biophysics, Center for Single Molecule Biophysics, SUNY at Buffalo, Buffalo, New York 14214
| | - Frederick Sachs
- The Department of Physiology and Biophysics, Center for Single Molecule Biophysics, SUNY at Buffalo, Buffalo, New York 14214
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Waseem TV, Kolos VA, Lapatsina LP, Fedorovich SV. Hypertonic shrinking but not hypotonic swelling increases sodium concentration in rat brain synaptosomes. Brain Res Bull 2007; 73:135-42. [PMID: 17499647 DOI: 10.1016/j.brainresbull.2007.03.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2007] [Accepted: 03/01/2007] [Indexed: 11/20/2022]
Abstract
Neurotransmitter release is dependent on both calcium and sodium influx. Hypotonic swelling and hypertonic shrinking of neurons evokes calcium-independent exocytosis of neurotransmitters into the synaptic cleft. To date, there are not too much data available on relationship between extracellular osmolarity and sodium concentration in presynaptic endings. In the present study we investigated the effects of hypotonic swelling and hypertonic shrinking on sodium levels, as measured using fluorescent dyes SBFI-AM and Sodium Green in rat brain synaptosomes. Reduction of incubation medium osmolarity from 310 to 230 mOsm did not raise the intrasynaptosomal sodium concentration. An increase of osmolarity from 310 to 810 mOsm is accompanied by a dose-dependent elevation of sodium concentration from 8.1+/-0.5 to 46.5+/-2.8mM, respectively. This effect was insensitive to several channel inhibitors such as: tetrodotoxin, an inhibitor of voltage-gated sodium channels, bumetanide, an inhibitor of Na(+)/K(+)/2Cl(-) cotransport, gadolinium, an inhibitor of nonselective mechanosensitive channels, ruthenium red, an inhibitor of transient receptor potential channel and amiloride, an inhibitor of epithelial sodium channel/degenerin. Additionally, using the fluorescent dye BCECF-AM, we have shown that hypertonic shrinking caused a dose-dependent acidification of intrasynaptosomal cytosol, which suggests that the Na(+)/H(+) exchanger is not involved in the effect of increased osmolarity on cytosolic sodium levels. The increase in intrasynaptosomal sodium concentrations following increases in osmolarity is probably due to sodium influx through another sodium channels.
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Affiliation(s)
- Tatyana V Waseem
- Institute of Biophysics and Cell Engineering, Akademicheskaya Street, 27, Minsk 220072, Belarus
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42
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Karabaliev M. Effects of divalent cations on the formation and structure of solid supported lipid films. Bioelectrochemistry 2007; 71:54-9. [PMID: 17383944 DOI: 10.1016/j.bioelechem.2007.02.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2006] [Revised: 01/23/2007] [Accepted: 02/16/2007] [Indexed: 11/25/2022]
Abstract
The interaction of glassy carbon-supported thin wetting films of lecithin with some divalent cations is investigated by impedimetry and voltammetry. The influence of Ca2+, Mg2+, and Mn2+ on the film structure is explored in two different cases--the divalent cations are added to the electrolyte either before or after the formation of the film. When the film has been previously formed, the addition of divalent cations in millimolar concentrations leads to changes in the passive electrical parameters and the blocking properties of the films. On the one hand the dielectric properties of the film measured in 0.1 M KCl seem to improve after the interaction with divalent cations--the film capacitance decreases, the resistance and resistivity of the film increase. On the other hand the increase of the redox current in the presence of 1 mM Fe(CN)6(3-/4-) in the electrolyte suggests the formation of some defects in the lipid structure of the film after the action of divalent cations. It is shown that the amount of these defects could be significantly decreased when the divalent cations are present in the electrolyte solution before the film formation. The effect of divalent cations on the film stability is tested by applying negative potential to the film. In 0.1 M KCl the films are not stable at potential of - 0.8 V (vs. Ag/AgCl) and are destroyed. The addition of divalent cations stabilizes the films and at certain millimolar concentrations the films remain intact after the action of the negative potential. The effect of Mn2+ is more pronounced, the Ca2+ and Mg2+ have smaller commensurate effect. It is proposed that the changes in the films' properties could be related with more tight packing of the lipid molecules with the divalent cations inserted in the film and that some defects could be opened during the rearrangement of the lipids when the film has been previously formed.
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Affiliation(s)
- Miroslav Karabaliev
- Department of Physics and Biophysics, Faculty of Medicine, Trakia University, 11 Armeiska, Stara Zagora 6003, Bulgaria.
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43
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Petrov E, Martinac B. Modulation of channel activity and gadolinium block of MscL by static magnetic fields. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2006; 36:95-105. [PMID: 17089151 DOI: 10.1007/s00249-006-0109-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2006] [Revised: 09/18/2006] [Accepted: 10/10/2006] [Indexed: 11/28/2022]
Abstract
The magnetic field of the Earth has for long been known to influence the behaviour and orientation of a variety of living organisms. Experimental studies of the magnetic sense have, however, been impaired by the lack of a plausible cellular and/or molecular mechanism providing meaningful explanation for detection of magnetic fields by these organisms. Recently, mechanosensitive (MS) ion channels have been implied to play a role in magnetoreception. In this study we have investigated the effect of static magnetic fields (SMFs) of moderate intensity on the activity and gadolinium block of MscL, the bacterial MS channel of large conductance, which has served as a model channel to study the basic physical principles of mechanosensory transduction in living cells. In addition to showing that direct application of the magnetic field decreased the activity of the MscL channel, our study demonstrates for the first time that SMFs can reverse the effect of gadolinium, a well-known blocker of MS channels. The results of our study are consistent with a notion that (1) the effects of SMFs on the MscL channels may result from changes in physical properties of the lipid bilayer due to diamagnetic anisotropy of phospholipid molecules and consequently (2) cooperative superdiamagnetism of phospholipid molecules under influence of SMFs could cause displacement of Gd(3+) ions from the membrane bilayer and thus remove the MscL channel block.
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Affiliation(s)
- Evgeny Petrov
- School of Biomedical Sciences, University of Queensland, St Lucia, Brisbane, QLD 4072, Australia
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44
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Hamill OP. Twenty odd years of stretch-sensitive channels. Pflugers Arch 2006; 453:333-51. [PMID: 17021800 DOI: 10.1007/s00424-006-0131-0] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Accepted: 06/27/2006] [Indexed: 01/15/2023]
Abstract
After formation of the giga-seal, the membrane patch can be stimulated by hydrostatic or osmotic pressure gradients applied across the patch. This feature led to the discovery of stretch-sensitive or mechanosensitive (MS) channels, which are now known to be ubiquitously expressed in cells representative of all the living kingdoms. In addition to mechanosensation, MS channels have been implicated in many basic cell functions, including regulation of cell volume, shape, and motility. The successful cloning, overexpression, and crystallization of bacterial MS channel proteins combined with patch clamp and modeling studies have provided atomic insight into the working of these nanomachines. In particular, studies of MS channels have revealed new understanding of how the lipid bilayer modulates membrane protein function. Three major membrane protein families, transient receptor potential, 2 pore domain K(+), and the epithelial Na(+) channels, have been shown to form MS channels in animal cells, and their polymodal activation embrace fields far beyond mechanosensitivity. The discovery of new drugs highly selective for MS channels ("mechanopharmaceutics") and the demonstration of MS channel involvement in several major human diseases ("mechanochannelopathies") provide added motivation for devising new techniques and approaches for studying MS channels.
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Affiliation(s)
- O P Hamill
- Neurosciences and Cell Biology, UTMB, Galveston, TX, 77555, USA.
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Sabín J, Prieto G, Sennato S, Ruso JM, Angelini R, Bordi F, Sarmiento F. Effect of Gd3+ on the colloidal stability of liposomes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 74:031913. [PMID: 17025673 DOI: 10.1103/physreve.74.031913] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2006] [Revised: 07/24/2006] [Indexed: 05/12/2023]
Abstract
Lanthanide ions such as La3+ and Gd3+ are well known to have large effects on the structure of phospholipid membranes. Unilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) were prepared by sonication method and confirmed by transmission electron microscopy. The effects of concentration of gadolinium ions Gd3+ on DPPC unilamellar vesicles in aqueous media were studied by different techniques. As physical techniques, photon correlation spectroscopy, electrophoretic mobility, and differential scanning calorimetry were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersities values were observed as Gd3+ concentration increases, suggesting that this cation induces the aggregation of vesicles. Electrophoretic mobility measurements on unilamellar vesicles as a function of Gd3+ ion concentration show that the vesicles adsorb Gd3+ ions. Above Gd3+ concentrations of 0.1 mol dm-3, the zeta potential and light scattering measurements indicate the beginning of aggregation process. For comparison with similar phospholipids, the zeta potential of phosphatidylcholine interacting with Gd3+ was measured, showing an analogous behavior. Differential scanning calorimetry has been used to determine the effect of Gd3+ on the transition temperature (Tc) and on the enthalpy (DeltaHc) associated with the process.
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Affiliation(s)
- Juan Sabín
- Grupo de Biofísica e Interfases, Departamento de Física Aplicada, Facultade de Física, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain
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46
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Chapter 11 Elasticity and Electrostatics of Amphiphilic Layers: Current State of the Theory and the Experiment. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/s1554-4516(06)05011-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
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47
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Copland IB, Post M. Stretch-activated signaling pathways responsible for early response gene expression in fetal lung epithelial cells. J Cell Physiol 2006; 210:133-43. [PMID: 16998809 DOI: 10.1002/jcp.20840] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
High-tidal volume ventilation has been shown to increase the expression of several inflammation-associated genes prior to overt physiologic lung injury. Herein, using an in vitro stretch system, we investigated the mechanotransduction pathways involved in ventilation-induced expression of these early response genes (i.e., early growth response gene (Egr)1, heat-shock protein (HSP)70, and the pro-inflammatory cytokines interleukin (IL)-1beta, IL-6, and MIP-2). Mechanical stretch of fetal lung epithelial cells activated various signaling pathways, resulting in transient or progressive increases in gene expression of the early response genes. The transient increase in Egr1 and IL-6 expression was mediated via p44/42 mitogen-activated protein kinase (p44/42 MAPK), while nuclear factor-kappaB (NF-kappaB) was responsible for the sustained and progressive increase in expression of HSP70 and MIP-2. Blockage of Egr-1 expression did not affect the upregulation of IL-6, HSP70, MIP-2, and itself by stretch. Inhibition of calcium mobilization abolished stretch-induced p44/42 MAPK activation and NF-kappaB nuclear translocation as well as increased expression of all early response genes. Similar results were obtained with an inhibitor of Ras. These results suggest that mechanical stretch of fetal lung epithelial cells evokes a complex network of signaling molecules, which diverge downstream to regulate the temporal expression of a unique set of early response genes, but upstream converge at calcium. Thus, calcium mobilization may be a point of hierarchical integration of mechanotransduction in lung epithelial cells.
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Affiliation(s)
- Ian B Copland
- Lung Biology Program, Hospital for Sick Children Research Institute, University of Toronto, Ontario, Canada
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Morris CE, Juranka PF, Lin W, Morris TJ, Laitko U. Studying the mechanosensitivity of voltage-gated channels using oocyte patches. Methods Mol Biol 2006; 322:315-29. [PMID: 16739733 DOI: 10.1007/978-1-59745-000-3_22] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The mechanosensitivity of voltage-gated (VG) channels is of biophysical, physiological. and pathophysiological interest. Xenopus oocytes offer a critical advantage for investigating the electrophysiology of recombinant VG channels subjected to membrane stretch, namely, the ability to monitor macroscopic current from membrane patches. High-density channel expression in oocytes makes for macroscopic current in conventional-size, mechanically sturdy patches. With the patch configuration, precisely the same membrane that is voltage-clamped is the membrane subjected to on-off stretch stimuli. With patches, meaningful stretch dose responses are possible. Experimental design should facilitate within-patch comparisons wherever possible. The mechanoresponses of some VG channels depend critically on patch history. Methods for minimizing and coping with interference from endogenous voltage-dependent and stretch-activated endogenous channels are described.
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49
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Suchyna TM, Besch SR, Sachs F. Dynamic regulation of mechanosensitive channels: capacitance used to monitor patch tension in real time. Phys Biol 2005; 1:1-18. [PMID: 16204817 DOI: 10.1088/1478-3967/1/1/001] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
All cells, from bacteria to human, are mechanically sensitive. The most rapid of these membrane protein transducers are mechanosensitive ion channels, ionic pores in the membrane that open and close in response to membrane tension. In specific sensory organs, these channels serve the senses of touch and hearing, and inform the central nervous system about the filling of hollow organs such as the bladder. Non-specialized cells use these channels to report on changes in cell volume and local strain. To preserve dynamic sensitivity, sensory receptors adapt to steady-state stimuli. Here we show that in rat astrocytes, the most abundant cells in the brain, this apparent adaptation to the stimulus is actually an inactivation. We have been able to track the time course of local strain by measuring attofarad changes in membrane capacitance and show that it is not correlated with loss of channel activity. The reduction in current with time is caused by an increased occupancy of low conductance states, and a reduction in the probability of opening, not a relaxation of local stress. The occupancy of these substates depends on the integrity of the cell's cytoplasm. However, while disruption of the cytoskeleton leads to a loss of inactivation, it leaves activation unaffected. The activation process is voltage-insensitive, closely correlated with changes in capacitance, and seems to arise solely from stress in the bilayer. The inactivation rate decreases with depolarization, and kinetic analysis suggests that the process involves multiple cytoplasmic ligands. Surprisingly, multivalent ions such as Gd(+3) and Ca(+2) that bind to the lipids and affect channel gating, do not affect the strain-induced increase in membrane capacitance; contrary to expectations, membrane elasticity is unchanged.
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Affiliation(s)
- Thomas M Suchyna
- Department of Physiology and Biophysics, SUNY at Buffalo, Buffalo, NY 14214, USA.
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50
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Tousova K, Vyklicky L, Susankova K, Benedikt J, Vlachova V. Gadolinium activates and sensitizes the vanilloid receptor TRPV1 through the external protonation sites. Mol Cell Neurosci 2005; 30:207-17. [PMID: 16099171 DOI: 10.1016/j.mcn.2005.07.004] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2005] [Revised: 06/22/2005] [Accepted: 07/07/2005] [Indexed: 11/30/2022] Open
Abstract
Gadolinium is a recognized blocker of many types of cation channels, including several channels of the transient receptor potential (TRP) superfamily. In this study, we demonstrate that Gd(3+), in addition to its blocking effects, activates and potentiates the recombinant vanilloid receptor TRPV1 expressed in HEK293T cells. Whole-cell currents through TRPV1 were induced by Gd(3+) with a half-maximal activation achieved at 72 microM at +40 mV. Gd(3+), at concentrations up to 100 microM, lowered the threshold for heat activation and potentiated the currents induced by capsaicin (1 microM) and low extracellular pH (6). Higher concentrations of Gd(3+) (>300 microM) blocked the TRPV1 channel. Neutralizations of the two acidic residues, Glu600 and Glu648, which are the key residues conferring the proton-sensitivity to TRPV1, resulted in a loss of Gd(3+)-induced activation and/or a reduction in its potentiating effects. A trivalent nonlanthanide, Al(3+), that possesses much a smaller atomic mass than Gd(3+) blocked but did not activate or sensitize the TRPV1 channel. These findings indicate that Gd(3+) activates and potentiates the TRPV1 by neutralizing two specific proton-sensitive sites on the extracellular side of the pore-forming loop.
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Affiliation(s)
- Karolina Tousova
- Department of Cellular Neurophysiology, Institute of Physiology, Academy of Sciences of the Czech Republic, Vídenská 1083, 14220 Prague 4, Czech Republic
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